RESUMO
Background Subways are typical congregate settings and may facilitate aerosol transmission of viruses. However, quantified transmission probability estimates are lacking. Purpose To model spread and diffusion of respiratory aerosols in subways by simulation and calculation of infection probabilities. Methods The internal environment of carriages of Shanghai Metro Line 10 was used to establish a study scene. The movement of tiny particles was simulated using the turbulent model. Trend analysis of infection probabilities and viral quantum doses was conducted in a closed subway carriage scene by a quantum emission-infection probability model. Results Under a typical twelve-vent air conditioning configuration, respiratory droplet aerosols within a subway carriage dispersed rapidly throughout various regions due to airflow, with limited short-term diffusion to other carriages. Concurrently, owing to the uncertainty of airflow patterns, the airflow might circulate and converge within carriages, causing delayed outward dispersion or hindered dispersion of droplet aerosols upon entry into these zones. Passengers boarding the carriage could exacerbate the formation of these zones. When the air conditioning system functioned adequately (air exchange rate=23.21 h−1), the probability of a virus carrier transmitting the virus to other passengers within the same carriage via aerosol transmission was approximately 3.8%. However, in the event of air conditioning system failure (air exchange rate=0.5 h−1), this probability escalated dramatically to 30%. Furthermore, a super-spreader (with virus spreading exceeding 90% of the average) elevated the infection probability to 14.9%. Additionally, due to the complexity of turbulence within the carriage, if local diffusion occurred in 1/2 zones of a carriage, the anticipated infection probability would increase to 8.9%, or during the morning or evening rush hours leading to elevated aerosol concentrations, the infection probability would rise to 4.7%. The subway transmission probability for common coronaviruses diminished to as low as 0.9%. Conclusion Combined computational fluid dynamics and infection probability analysis reveals that in the prevalent twelve-vent air conditioning configurations, despite being a major transportation hub with substantial spatial-temporal overlap, the internal space of subway carriages exhibits a certain level of resistance to virus aerosol transmission owing to built-in ventilation capabilities. However, turbulence and passenger positioning may lead to localized hovering of droplet aerosols, thereby increase the risk of virus transmission. Furthermore, super-spreaders, poor operational status of built-in air conditioning system, and high passenger volume at morning or evening peak hours exert profound effects on virus transmission and infection probability.
RESUMO
ObjectiveTo construct an evaluation index system for the development of district-level disease prevention and control centers according to the requirements of the modernization of Shanghai’s disease control system and public health work practices， and to comprehensively assess the construction and development of district-level disease prevention and control institutions. MethodsAccording to the national and municipal requirements for the development of disease prevention and control institutions， an index framework was proposed through literature search and expert interviews. 39 representative experts in the field of public health at the national， provincial， and municipal （district） levels were selected to participate in the consultation and construction of the index system. The authority coefficient， the coefficient of variation， etc. were used to carry out quality control and determination of each index on the Delphi method. ResultsThe questionnaire response rate was 100%， the expert authority coefficient was 0.86，the degree of familiarity was 0.79， and the judgment basis was 0.92. The coefficients of variation of the necessary indicators in the index system were all <0.25 in the dimension of importance， and there were statistical differences in the statistical test of Kendall’s W coordination coefficients at all levels and dimensions （all P<0.001）. After multiple rounds of consultation， experts reached a consensus， forming a development evaluation index system of district-level CDCs with 6 first-level indicators， 24 second-level indicators， and 105 third-level indicators （including 63 necessary indicators and 42 recommended indicators）. ConclusionThe evaluation index system of Shanghai district-level CDCs based on the Delphi method has good authority， reliability， sensitivity and operability. This indicator system can effectively support the development of Shanghai district-level CDCs， and can be used for evaluation at multiple levels and in an all-round way in the future. The evaluation results can provide an evidence-based basis for the modernization of the disease prevention and control system and the continuous and dynamic updating of the development goals in the future.